Optical networks are starting to utilize reconfigurable optical-add drop multiplexers (R-OADMs) to switch wavelengths in a wavelength division multiplexed system (WDM). R-OADMs provide the ability to switch any wavelength without the need to perform an electrical conversion. Additionally, R-OADMs provide network operators advantages with regards to reconfigurations, network routing, power balancing, and the like. As such, network operators are deploying R-OADM devices in metropolitan and long-haul optical networks.
R-OADMs typically utilize either a wavelength-switched architecture or a broadcast-and-select architecture. The wavelength-switched architecture consolidates the wavelength switching and multiplex/de-multiplex (MUX/DEMUX) functions within the same functional block (i.e. a wavelength selective switch (WSS)), making the wavelength-switched architecture relatively less complex and less expensive (requiring N switches for N node degrees). The broadcast-and-select architecture, on the other hand, requires MUX/DEMUX functions that are independent from the wavelength switching function, making the broadcast-and-select architecture relatively more complex and expensive (requiring N×(N−1) wavelength blockers for N node degrees). These architectures are inherently contradictory. In the wavelength-switched architecture, an inbound (or added) wavelength is switched to either an output port or a drop port. If switched to a drop port, the inbound (or added) wavelength cannot reach additional subscribers, as required by the broadcast-and-select architecture. Users may re-generate and transmit the received broadcast signal, but this requires the use of additional transceivers, increasing the number of components utilized and compromising overall system reliability. Thus, wavelength-switched R-OADMs do not support a wavelength broadcasting function, as broadcast-and-select R-OADMs do.
In modern networks, bandwidth growth is being driven in metropolitan and long-haul optical networks by video transport as high-definition television (HDTV), video on-demand (VOD), and other video-related services proliferate. Broadcast video signal distribution is inherently asymmetric. A small number of video signals are received by a large number of subscribers, the subscribers typically transmitting no signals. For example, SONET/SDH systems can utilize a drop-and-continue architecture allowing a single signal, such as an OC-12/STM-4, OC-48/STM-64, etc., to drop at multiple locations and continue. With regard to optical equipment supporting video signal distribution, WDM networks typically utilize the broadcast-and-select architecture for R-OADMs, sacrificing with respect to component complexity and expense.
Thus, what is needed in the art is a wavelength-switched R-OADM with wavelength broadcasting capability, such that unidirectional video signal distribution and the like can be performed without sacrificing component complexity and expense.